Photographic processing can be carried out at a very simple technological level, where a single operator working with acquired skill in a dark room manipulates the film or paper, passing it through trays containing the necessary chemicals for necessary time intervals, and relying on dexterity to complete the procedures before solution temperatures depart unacceptably from the appropriate values. This is the procedure of the typical photographic amateur, and highly successful results can be obtained by competent amateurs who have to contend with no press of time for commercial practicality.
At the other extreme, photgraphic processing can be carried out on a wholesale scale, where wholly automatic machines handle enormous masses of photographic material with speed and competence, where dark room operation and human operator skill are held to a minimum, and where large volumes of chemicals are dispensed and utilized with continuous control of composition, temperature and time intervals to give a result that is uniformly successful, if not uniformly superior. Naturally such machines are large, expensive and intricate, and hence are practical only for the processor on a commercial scale.
Attempts have been made to produce machines useful to the serious professional photographer and yet within his reach financially. Such machines have in the past required a great deal of manual operation, and a great deal of operation under dark room conditions, and have often resulted in unsatisfactory results by reason of contamination of one liquid with small quantities of liquid from a previous process.